suseda

1. neighbour
   Suseda sa trećeg sprata nam je donela kolače. — Our neighbour from the third floor brought us some cakes.
   Zamolila sam susedu da mi zalije cveće. — I asked my neighbour to water my plants.
2. (in class, transport) woman sitting next to someone; deskmate
   Moja suseda u autobusu je celim putem pričala telefonom. — The woman next to me on the bus was on the phone the whole way.

In everyday speech "komšinica" is more common.